1. Field of the Invention
The present invention relates to a laser light source device that uses a laser light source.
2. Description of the Related Art
Vehicle lamps require a high brightness light source in order to illuminate a long distance with a sufficient intensity of light. Vehicle lamps having a laser light source device have been proposed in recent years, which combine a semiconductor laser that emits blue laser light and a fluorescent member that emits light when excited by the blue laser light from the semiconductor laser.
Japanese Patent Application Publication (Kokai) No. 2008-10228 describes a laser light source device. This laser source device includes a surface emitting laser element having a plurality of light emitting parts arranged on the surface of the surface emitting laser element, a mask having mask apertures formed in the surface of the surface emitting laser element to expose the light emitting parts, and a fluorescent member filled inside the mask apertures.
FIG. 1A of the accompanying drawings shows the shape of a beam spot Sp1 formed by laser light emitted from a common laser diode 200 on a projection surface orthogonal to the optical axis of the laser light. FIG. 1B of the accompanying drawings shows the brightness distribution of the beam spot. As depicted in FIG. 1A, the beam spot Sp1 has an oval shape, its width AH in direction X parallel to a pn joint surface of the laser diode 200 being smaller than the width AV in direction Y vertical to the pn joint surface. As shown in FIG. 1B, the light intensity distribution of the beam spot Sp1 is a symmetric Gaussian distribution, wherein the light intensity is the highest at the optical axis center, and decreases smoothly outward from the optical axis center.
The laser light source device used in a vehicle lamp generates white light by irradiating light having such a Gaussian light intensity distribution to the fluorescent member through a condenser lens. The white light also has a Gaussian light intensity distribution, so that the light intensity at both ends of the light emission area is relatively low. In vehicle lamp applications, an optical system including a lens and a reflector is used to project light from the light source onto the road surface. The illuminance on the road surface is inversely proportional to the square of the distance from the light source. Thus, if end areas of the light source that illuminate a distant road surface have a relatively low brightness, the illuminance of the distant road surface will be lower than that near the vehicle. As a result, the bright/dark boundary commonly referred to as a “cutoff line” will be blurry, and the visibility in a distance will be low. For this reason, commonly, a light shield member such as a shade is provided in front of the light source to shut off part of light from the light source to make the bright/dark boundary clearer. This, however, significantly lowers the light utilization efficiency. Some laser diodes have a beam spot that is not oval as that of the surface emitting laser shown in FIG. 1A, but they have the same problem because they have a similar light intensity distribution in which the light intensity is highest at the optical axis and smoothly decreases outward.